Time to build up primary fuel pressure

[Horsebox]

Hi,

If the car has sat for a week or so almost always on first start it will fire up immediately, presumably on the CSV fuel, and then struggle and bog down for several seconds, sometimes dying, before bursting back into life and then running as normal.

I had some running problems recently, now fixed, so while the fuel pressure testing kit was plumbed in I measured how long it took the primary pressure to come up to spec: after sitting for maybe 10 days it took 7 seconds! It holds rest pressure very well so I don't think there is a leak in the accumulator.

I seem to remember a post where somebody here did the same test and measured about half a second to build up pressure. Big difference, and might explain my bogging down when it's first started.

Any ideas? Anybody with any experience of the accumulator failing in this way? I.e. no leak but for some reason takes ages to come up to pressure.

Another thing I noticed was when depressurising the fuel system by operating the frequency valve (rather than opening the lines under rest pressure). You could hear the accumulator "clank" over and over as the FV let the pressure back into the tank.

Cheers,

Mark

[DMCVegas]

Press and hold your accelerator pedal down a ¼ of the way while cranking, and see if that make a difference to start with.

[Horsebox]

Press and hold your accelerator pedal down a ¼ of the way while cranking, and see if that make a difference to start with.

That's what I always do.

[Bitsyncmaster]

Hi,

If the car has sat for a week or so almost always on first start it will fire up immediately, presumably on the CSV fuel, and then struggle and bog down for several seconds, sometimes dying, before bursting back into life and then running as normal.

I had some running problems recently, now fixed, so while the fuel pressure testing kit was plumbed in I measured how long it took the primary pressure to come up to spec: after sitting for maybe 10 days it took 7 seconds! It holds rest pressure very well so I don't think there is a leak in the accumulator.

I seem to remember a post where somebody here did the same test and measured about half a second to build up pressure. Big difference, and might explain my bogging down when it's first started.

Any ideas? Anybody with any experience of the accumulator failing in this way? I.e. no leak but for some reason takes ages to come up to pressure.

Another thing I noticed was when depressurising the fuel system by operating the frequency valve (rather than opening the lines under rest pressure). You could hear the accumulator "clank" over and over as the FV let the pressure back into the tank.

Cheers,

Mark

With zero rest pressure it took less than 1.5 seconds to bring the primary pressure back up to 75 PSI. I have the original size accumulator so the smaller one would be faster. I used that test to set my prime time in my RPM relay.

Yes my accumulator will clank as I release rest pressure.

[DMC5180]

The clanking is just the spring inside the accumulator relaxing.

The stumbling after CSI fuel burn off is likely because you have some leaking injectors that allow the injector lines to empty out over time. It takes several seconds at idle for the fuel lines to refill and start spraying into the cylinder to fire again.

It might be to your benefit, to have the injectors serviced by a vendor there may be some deposits keeping the injector pintle from seating or they are just worn out.


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[DMCVegas]

Hmm... You haven't been tinkering with the fuel mixture, have you? Because this sounds like a bad mixture. Either from a bad injector, or a bad CO Screw adjustment.

[Horsebox]

With zero rest pressure it took less than 1.5 seconds to bring the primary pressure back up to 75 PSI.

I just looked at the videos I took of the pressure gauge again, not good to rely on memory. It seems it was only after I left the car unstarted for ten days that it took the whole 7 seconds to build the primary pressure.

When I went back for another play the next day, as you say 1.5 seconds or so from zero pressure. Difficult to count properly as it happens so quick.

[Horsebox]

The clanking is just the spring inside the accumulator relaxing.

The stumbling after CSI fuel burn off is likely because you have some leaking injectors that allow the injector lines to empty out over time. It takes several seconds at idle for the fuel lines to refill and start spraying into the cylinder to fire again.

It might be to your benefit, to have the injectors serviced by a vendor there may be some deposits keeping the injector pintle from seating or they are just worn out.


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The injectors are brand new, although I agree that doesn't mean they work right. If they were leaking into the intake then wouldn't I see that in a quickly dropping rest pressure? And if they were leaking at the banjo connections I would see leaking fuel over the manifold? Neither of which I see.

It's a good point, I might just pull the injectors and put them in jars to see what happens.

[Horsebox]

Hmm... You haven't been tinkering with the fuel mixture, have you? Because this sounds like a bad mixture. Either from a bad injector, or a bad CO Screw adjustment.

I might have had a bit of play :-) But always with an exhaust gas analyser plugged in so I could see what I was doing to it. Currently 1.5%CO and ran really well on a drive this afternoon. Will be interesting to see how it cold starts/warms up tomorrow after being left on the naughty step outside -4C all night.

[DMC5180]

Pretty much that's what you need to do. It only takes a couple to make the engine run like crap.

I have the same issue on my car. It showed up right after I installed New injectors. For me it's just a minor nuisance. If I drove the car more regularly I'd probably never notice it.

It typically shows up after a couple weeks of sitting. I keep telling myself I'm gone look into it. But have yet to do it.

The issue with pulling injectors to see how long it takes is a tough one because fuel evaporates quickly. Meaning you could set up jars to catch fuel that weeps slowly only to have it dry up quickly and you'll never know how much they leak if it's really slow.

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[Horsebox]

Yeah I should probably just leave it too. At the end of the day it starts up after the second attempt worst case and then runs perfectly for the rest of the day. Not bad for a 35 yr old car I guess. It's annoying knowing that the answer is simple and the thought that I'm just too lazy to figure it out...

[David T]

Yeah I should probably just leave it too. At the end of the day it starts up after the second attempt worst case and then runs perfectly for the rest of the day. Not bad for a 35 yr old car I guess. It's annoying knowing that the answer is simple and the thought that I'm just too lazy to figure it out...

Next time turn the key on and off once or twice before trying to start the motor. First time starting after sitting for a while does take a bit longer. Some cars start quicker than others. A lot of factors affect it. How strong the battery is, how quickly it turns over, the temperature, how fresh the fuel is, etc. Some start better if you step on the gas pedal 1/4, others don't need it. They all sputter a bit for a minute or so and then take the pedal well if in good tune.

[Horsebox]

Next time turn the key on and off once or twice before trying to start the motor.

Good plan. I might go one further for the sake of experiment and jump the RPM relay for 20 secs or so before the next few cold starts. It took maybe three or four attempts this morning to get it going after a cold soak on the naughty step at -8C. Once running it was fine and drove really well, better than ever actually, after tickling the mixture up to 2% CO.

[Bitsyncmaster]

Do you have a CAT? That can throw an error reading exhaust AFR. The error is not that great maybe .5 % AFR.

[Horsebox]

Do you have a CAT? That can throw an error reading exhaust AFR. The error is not that great maybe .5 % AFR.

No CAT, which makes life easier to measure the CO. The 0.5% is interesting. So the CAT halves the CO emissions.

If you fancy a chuckle read on. I just discovered that a PO had peeled back the harness at the CSV electrical connector, cut and swapped the two wires, and then covered it back up, despite the electrical connector being keyed so it can't be plugged in the wrong way. I can't think of any reason to do that other than sheer desperation...

I've corrected that and now have a working CSV for the first time since owning the car. Should help with the cold starts!

[DMC5180]

Always mind boggling to stuff like that. Nice find and fix.


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